PROJECT SUMMARY/ABSTRACT The broad aim of this research is to evaluate whether a brief and cost-effective value affirmation writing intervention reduces physical symptoms, stress and medication non-adherence among breast cancer patients taking aromatase inhibitors (AIs). The majority of postmenopausal women diagnosed with breast cancer will be prescribed an AI; and while effective, these medications lead to toxic physical symptom side effect profiles and poor adherence. Interventions that target these side effects and the stress they cause may lead to improved medication adherence and therefore improved survival rates for breast cancer patients taking AIs. In pilot work from our group and others, thinking or writing about important personal values in value affirmation interventions have been linked to fewer physical symptoms, decreased stress, and improved medication adherence. While promising, these initial studies had small samples or were cross sectional in nature, and did not evaluate potential neurobiological mechanisms for intervention effects. The proposed study will be a randomized controlled trial (RCT) comparing a 6-month, portable value affirmation writing intervention (N=125) to a control writing intervention (N=125) in breast cancer patients taking aromatase inhibitors. Participants will complete self-reported measures of physical symptoms, adherence and stress at baseline, post-intervention, and 6-month follow-up. Medication adherence will also be assessed via electronic pill bottle reporting and refill latency during the study period. As an exploratory mechanistic aim, a subsample of AI patients from the parent RCT (N=120, 60 per intervention arm) will complete their mid-intervention value affirmation or control writing task while undergoing functional MRI. Thus, the proposed study will test two specific aims and an exploratory aim to determine: if value affirmation writing reduces physical symptoms and stress (Aim 1), improves medication adherence (Aim 2), and if neural reward activation during value affirmation is a neurobiological mechanism for these benefits (Exploratory Aim 1). The proposed RCT has the potential to identify a powerful, cost-effective, and easy-to-implement value affirmation intervention for reducing symptoms, stress, and medication non-adherence in breast cancer patients taking AIs.